Method of preparing titanium, zirconium and tantalum



Jan. 21, 1958 R. J. FLETCHER 2,820,722

METHOD FOR PREPARING TITANIUM; ZIRCONIUM AND TANTALGM Filed se t. s,1954 2 Sheets-She'i -1 Jan. 21, 1958 R. J. FLETCHER 2,820,722

' METHOD FOR PREPARING TITANIUM, ZIRCONIUMYAND TANTALUM Filed Sept. 3,1954 2 Sheets-Sheet 2 Amswme A M/aka 1557015? United States Thisinvention relates enerally to a method for preparing metals which formweakly-bonded covalent halides, and, more particularly, to a method forpreparing titanium, zirconium, or tantalum, since these are the metalsof greatest commercial interest in the aboveriamed group. While myexperiments to date have not extended beyond the three metals justnamed, I believe the 'method's' described in this specification could,without difiiculty, be ap lied to the preparation of the other metalswhich form weakly-bonded covalent halides.

I In the conventional hot-wire or Van Arkel process for the preparationof titanium, the metal is desposited, by thermal dissociatioh, on a wireraised to red-heat in an atmosphere of the vapour of a weakly-bondedcovalent compound or titanium, usually the tetrachloride ortetr'aiodide. This" treatment" possesses certain disadvantages: (I) Itis virtually" impossible to build upa large ingot on the hot wire. (2.)The process cannot be made continuous owing to the progressive dilutionof the compound ('s'ay TiCL, or T-iI vapour by free chlorine or iodine.a

I have found that the Van Arkel titanium process can be improved torender it continuous and more productive, and that the improved processmay be expanded to embrace the preparation of those metals in additionto titanium which form weakly-bonded covalent halides, for example,zirconium and tantalum. i 7

My contribution to the art maybe generally defined as a method forcontinuously preparing titanium, or z-irconium, or tantalum, byremovably mounting a small body, preferably a wire or :pla'te,of thedesired metal in a closed vessel; establishing a high vacuum within thevessel; heating the small body while directing a halide (a chloride,bromide, or iodide) of the metal into the vessel as' a molecularbeamwhich is completely intercepted by the heated body, the body beingheated to a temperature in excess of the dissociation temperature of theselected metal halide so that the beam of the latter, upon contactingthe body, is broken up into (a); free metal, which is deposited on theheated body, and (b) a free halogen (chlorine, bromine, or iodine). Thefree halogen is removed as it is formed (-e. g., by pumping it ofi as agas, or by condensation followed by collection of the condensate); andthe body, after an in'got of desirable weight hasbeen formed thereongisremoved and replaced by a fresh body. I h p The invention embraces amodification of the process of the preceding paragraph. In thismodification 'a small body of the desired metal (titanium, zirconium, ortantalum.) i-s removably mounted in a closed metal vessel which isfilled With a gaseeus halide (a chloride, bromide, or iodide) of thedesired metal, which halide is'maintained at a reduced pressure, e. g.about 0.01 mm. to about 1mm. of mercury. Metal is then electrodepositedon the said small body by an electrolysis which involves the employmentof the metal vessel as the anode, the body of the desired metal as thecathode, and the gaseous metal halide ateiit as the electrolyte, and thepassage of a heavy current through the gaseous metal halide.

In drawings which illustrate embodiments of the invention:

Figure 1 is a diagrammatic illustration of one embodiment,

Figures 2 and 3 are diagrammatic illustrations of some what modifiedforms of the embodiment of Figure 1,

Figure 4 is a diagrammatic showing of modification of the inventiondependent upon electrolysis of a gaseous medium, and I Figure 5 is adiagrammatic showing of an embodiment similar to that shown in Figure 4,but modified by the inclusion of induction heating.

Considering first the case of Figure 1, reference numeral 10 indicates aclosed reaction vessel provided with a detachable end plate 11. Amandrel 12 is passed through a seal 13 in end plate 11 and is centrallydisposed within the vessel 10. Mandrel 12 carries at its inner endaplate 14 of titanium. Reference numeral 15 indicates a source oftitanium tetrachloride which may be fed from the source through areducing valve 16 and along a com duit 17 to a nozzle 18, which openswithin the reaction vessel and is directed towards the titanium plate14;

The vessel 10 is provided with a means for evacuating it andcontinuously pumping 01f any gases formed during the reaction. Thismeans consists of a conduit 19 leadingfrom the vessel, a gate valve 20,a high vacuum pump 21,- and a mechanical pump 22. The titanium plate 14is surrounded by an induction heating coil 23. The high frequency leadsto induction heating coil 23, have been labelled 24 and 25.

The apparatus shown in Figure 1. could be employed in the followingmanner in the preparation of titanium from titanium tetrachloride: V

The closed vessel 10 is first evacuated using the pumps 21 and 22. Thetitanium plate 14 is then heated by'the induction heating coil 23 to atemperature in excess of the dissociation temperature of titaniumtetrachloride. The

valve 16 is then opened to produce a jet of titanium tetra-' chloride atnozzle 18. The nozzle 13 isdesigned to produce a narrow jet which isdirected towards and Wholly intercepted by the heated plate 14. Thepressure within the vessel is kept at a low figure, preferably below.001 of mercury, so that the motion of the molecules of titaniumtetrachloride issuing from thejet is rectilinear and they form amolecular beam in their travel towards the plate. When the molecules oftitanium tetrachloride contact "the plate, the heated plate causesdissociation of the titanium tetrachloride into metallic titanium (whichadheres to the heated plate) and free chlorine; The free chlorine isremoved as it is formed, via gate valve 20, high vacuum pump 21 andmechanical pump 22. The

chlorine produced by the action must be removed so that the desired highvacuum conditions may be maintained inasmuch as they are essential tothe maintenance of the molecular beam; and it will be appreciated thatthe of a high vacuum also has the advantage of rendering negligible theprobability of the titanium absorbing any damaging quantity of chlorine,oxygen, nitrogen, or other gas, which might be present in the reactionvessel.

As the deposit of fresh titanium builds up on the plate v 14, theplate-carrying mandrel 12 is slowly withdrawn and is slowly axiallyrotated to ensure a uniform build up of the titanium. When a titaniumingot of suflicient size has been formed, the mandrel 12 carrying theingot is removed and replaced by a mandrel carrying a [fresh plate. inorder that the process may be carried; out

7 continuously, instead of employing a detachable end plate 11, a vacuumgate may be employed to facilitate removal of the titanium ingot auditsreplacement with a fresh plate. Alternatively, a reserve mandrelcarrying the fresh plate could be rotated into position on a capstan orthe like, or any other suitable mechanical arrangement could be employedto change the mandrel so that the process may be made continuous.

' In the discussion of Figure 1 given above, and in the discussion ofthe remaining figures which follows, for purposes of illustration, thepreparation of titanium from titanium tetrachloride is described. Itshould be clearly understood, however, that the process embraces theproduction of titanium from bromides and iodides thereof and theproduction of zirconium and tantalum from their chlorides, bromides andiodides. I do not recommend or claim the use of the fluorides of thesemetals. In case of titanium and titanium tetrachloride has been chosenbecause of the commercial importance of titanium and the readyavailability of titanium tetrachloride. Actually, aside fromconsiderations of availability and economics, I would prefer to workwith the tetrabromide or tetraiodide rather than the tetrachloridebecause of their lower dissociation temperatures. The use of thetetraiodides is also attractive since iodine lends itself to removal bycondensation rather than the pumping step illustrated in Figure 1.

The arrangement shown in Figure 2 is generally similar to thearrangement shown in Figure 1. However, it will be noted that inductionheating is dispensed with in Figure 2. It is possible to dispense withthe induction heating by establishing a marked potential differencebetween the nozzle 18 and the late 14. Connections for establishing thispotential difference have been indicated' at 26 and 27 in Figure 2; Theestablishment of this high potential difference between the nozzle andplate with the plate negative), induces a heavy electrical current fiowin the stream of gas directed from the nozzle 18 on to the plate 14.Under these circumstances, the wire is heated by positive ionbombardment. The positive ion bombardment has been found sufiicient toraise the temperature of the plate to a figure in excess of thedissociation temperatures of the metal halides contemplated by theinvention. Once again the titanium tetrachloride or other metal halide)is broken up into metallic titanium, which adheres to the heated plate14, and free chlorine, which is once again pumped otf as it is formed.The operation of the apparatus of Figure 2 is, therefore. seen to besimilar to the case of Figure 1, except for the fact that inductionheating is replaced by positive ion bombardment.

The arrangement shown in Figure 3 is simply a combination of thearrangement shown in Figures 1 and 2, i. e. both positive ionbombardment and induction heating are employed to heat the plate uponwhich the titanium is deposited. The establishment of a potentialdifference between the plate and the nozzle is not only of value in thatit results in heating of the plate, but is also useful in that itinsures attraction and adherence of titanium to the plate. When anelectrical field and positive ion bombardment are employed, as in thecases of Figures 2 and 3, the vacuum should not be as high as in thecase of Figure 1, which depends for its success upon the establishmentof a molecular beam of the metal halide. Where an electrical field isemployed, as in Figures 2 and 3, I recommend operating at a reducedpressure of from about 1 mm. to about .01 mm. of mercury. A vacuum ashigh as that employed in Figure 1 would militate against the desiredcurrent fioW. However, the residual gas pressure must be sufficientlylow for the desired ionization of the metal halide.

Turning now to the arrangement shown in Figure 4, a is a closed metalvessel having a removable end plate 11a. 12a is a mandrel, 13a a sealand 14a a plate or-wire of titanium. 15a is a source of titaniumtetrachloride, 17a a conduit leading into the vessel 10a, and 16a is aflow-controlling valve in this conduit. Elements 19a, 20a, 21a and 22aare respectively, a conduit, gate valve, high vacuum pump and mechanicalpump for initially evacuating the shell 10a and, at the end of thereaction, drawing off free chlorine produced during the reaction. Thearrangement shown in Figure 4 is intended to be run as a batch processalthough the arrangement can be readily modified for continuousoperation. The arrangement of Figure 4 would be operated as follows:

The metal vessel 10a is evacuated, the gate valve 20a is then closed andthe valve 18a opened .so. that the metal vessel is filled with titaniumtetrachloride. The titanium tetrachloride should be at a reducedpressure of from about 1 to'.0l mm. of mercury. The electricalconnections 26a and 27a are then utilized to establish, in the plate1411, a high negative potential withrespect to the metal vessellOa. Theestablishment of this 'potential difierence causes a heavy electricalcurrent to pass between the metal vessel 10a and the titanium plate 14a.Once again the titanium plate is heated by positiveion bombardment to atemperature'in excess of the dissociation temperature of the titaniumtetrachloride. The titanium tetrachloride decomposes into free titanium,which adheres to the plate, and freechlorine. When a batch of titaniumtetrachloride has been treated, the mandrel 12a is withdrawn forrecovery of the titanium ingot built up upon the plate 14a, and the freechlorine is pumped off and recovered. The process could be renderedcontinuous by slowly withdrawing the mandrel, replacing the ingot with anew plate Where necessary; and by continuously feeding in titaniumtetrachloride and pumping off free chlorine.

' The arrangement shown in Figure 5 is similar to the arrangement shownin Figure 4 except for the fact that an induction heating coil 23a,having high frequency leads 24a and 25a, is provided to assist in theheating of the plate 14a. This particular arrangement has been foundvaluable in cases where the dissociation temperature of the metal halideis high, or other conditions militate against raising the plate 14:: tothe desired temperature. Since the arrangement of Figure 5 is similar tothe arrangement of Figure 4, except for the inclusion of the inductionheating means, further description of Figure 5 appears to beunnecessary.

It will be noted that the operation of the arrangements of Figures 4 and5 is essentially an electrolysis procedure wherein the metal shell isemployed as the anode, plate 14a is employed as the cathode, and themetal halide, e. g. titanium tetrachloride, is employed as theelectrolyte. The positive ions are carried to the cathode where theyadhere to form a deposit of metallic titanium.

It is particularly interesting to note that this electrolysis procedureinvolving ionization of the metal halide does not depend for itseffectiveness upon thermal dissociation of the metal halide. I haveactually determined that the electrolysis procedure may be carried outwithout any substantial heating of the plate 14a, and definitely withoutheating it to a temperature anything like the dissociation temperatureof the metal halide employed as the electrolyte. Where specialconditions make it desirable to effect the electrolysis with the platecold, precautions must be taken to avoid heating of the plate bypositive ion bombardment. The special precautions which may be employedinclude the water cooling of the plate or employment of a massivemandrel (for heat dissipation) in conjunction with low powerdissipation. The special conditions referred to above include thepreparation of high purity titanium free of gas inclusions, or thepreparation of titanium having special metallurgical properties whichwould be adversely affected by formation of the titanium at hightemperatures.

What I claim is:

A method for continuously preparing a metal selected from the groupconsisting of titanium, zirconium, and tantalum, which comprisesremovably mounting a small body of the desired metal in a closedreaction vessel; reducing the" pressure within said vessel to a value ofat most 1 mm. of mercury; heating said body by positive ion bombardmentWhile continuously directing a molecular beam of a halide of the metalthrough a jet orifice into said vessel and onto said heated body, thecross sectional area of said molecular beam at said heated body beingwithin the surface of said heated body nearest said jet orifice, saidmetal halide being selected from the group consisting of the chlorides,bromides, and iodides of the desired metal, and the body being heated toa temperature in excess of the dissociation temperature of the selectedmetal halide; continuously removing from said vessel free halogen formedin the region of said heated body by thermal dissociation of said metalhalide in accordance with the equation XY,,- X+nY wherein:

X is selected from Ti, Zr and Ta, Y is selected from I, Br and Cl, and nis an integer corresponding to the valency of X and periodicallyremoving said body and replacing it with a fresh body when anappreciable quantity of new metal has been deposited on the first bodyby the thermal dissociation of the metal halide.

References Cited in the file of this patent UNITED STATES PATENTS OTHERREFERENCES Powell et al.: The Deposition of Tantalum and Columbium fromTheir Volatilized Halides, Journal,

20 Electra-Chemical Society, vol. 93, 1948.

Campbell et al.: The Vapor-Phase Deposition of Refractory Materials.Journal, Electrochemical Society, vol. 96, 1949.

Childs et al.: Molybdenum Plating by Reduction of the PentachlorideVapor; Trans. of the A. S. M., vol. 43, May 29, 1950.

